A touch display panel generally uses optical fingerprint identification technology for fingerprint identification. Specifically, a plurality of pixel units in the touch display panel or each pixel unit may be provided with a photodetector configured to detect an optical signal reflected by fingerprint lines of a user when the pixel unit emits light and generate a current signal, so that the identifier in the touch display panel can identify the fingerprint lines based on the current signal.
In the related art, the photodetector may include a photosensitive element (the photosensitive element may be a photodiode). The photosensitive element is in a cutoff state when it's not irradiated by light, whereas it functions as a diode in an on state when it is irradiated by light and may output a current to the read line in the display panel. The larger the light intensity is, the larger the output current is. During fingerprint identification, since the fingerprint is formed by a series of fingerprint ridges and fingerprint valleys on the surface of the finger skin and the light refractive index of the fingerprint ridge differs from the that of the fingerprint valley, when the pixel unit emits light, the intensity of the light reflected from the fingerprint ridge is different from the intensity of light reflected from the fingerprint valley. Thus, the magnitude of the current finally generated by the photodetector is also different. Therefore, the identifier can determine the positions of the fingerprint ridge and the fingerprint valley according to the magnitude of the current, to realize the function of fingerprint identification.
However, since the optical signal detected by the photodetector is generally weak, the magnitude of the current converted from the optical signal is also small. When there is a leakage of current in the transistor in the photodetector, the current converted from the optical signal may be interfered, affecting the accuracy of fingerprint identification.